Method for recovering copper from copper-containing materials using direct electrowinning

ABSTRACT

A method for recovering copper from a copper-containing ore, concentrate, or other copper-bearing material to produce high quality cathode copper from a leach solution without the use of copper solvent extraction techniques or apparatus. A method for recovering copper from a copper-containing ore generally includes the steps of providing a feed stream containing comminuted copper-containing ore, concentrate, or other copper-bearing material, leaching the feed stream to yield a copper-containing solution, conditioning the copper-containing solution through one or more physical or chemical conditioning steps, and electrowinning copper directly from the copper-containing solution, without subjecting the copper-containing solution to solvent extraction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/737,420, which was filed on Dec. 15, 2003 and issued as U.S. Pat. No.6,972,107 on Dec. 6, 2005, which application is a continuation of U.S.patent application Ser. No. 10/238,399, which was filed on Sep. 9, 2002and issued as U.S. Pat. No. 6,663,689 on Dec. 16, 2003, whichapplication is a continuation of U.S. patent application Ser. No.09/912,921, which was filed on Jul. 25, 2001 and issued as U.S. Pat. No.6,451,089 on Sep. 17, 2002, the disclosures of which are incorporated byreference herein.

FIELD OF INVENTION

The present invention relates generally to a process for recoveringcopper from a copper-containing ore, concentrate, or othercopper-bearing material, and more specifically, to a process forproducing cathode copper without the use of solvent/solution extraction,ion exchange of copper, or related processes to refine and concentratethe copper-bearing solution.

BACKGROUND OF INVENTION

Hydrometallurgical treatment of copper containing materials, such ascopper ores, concentrates, and other copper-bearing materials, has beenwell established for many years. Currently, there exist many creativeapproaches to the hydrometallurgical treatment of these materials;however, common to almost all of the processes either now known or underdevelopment is the use of solvent extraction and electrowinning (SX-EW)for solution purification and copper recovery. Although SX-EW is notwithout its drawbacks, the proven success in the copper SX-EW field hasmade this approach standard for production of high quality copperproducts.

The traditional hydrometallurgical process for copper recovery involvesfirst leaching copper-containing material with an acidic solution,either atmospherically or under conditions of elevated temperature andpressure. The resultant process stream—the so-called pregnant leachsolution—is recovered, and in a solvent extraction (or solutionextraction, as it is sometimes called) stage, is mixed with an organicsolvent (i.e., an extractant), which selectively removes the copper fromthe pregnant leach solution. The copper-loaded extractant is then mixedwith an aqueous acid solution, which strips the copper from theextractant, producing a solution stream suitable for electrowinning.This resultant solution stream is highly concentrated and relativelypure, and typically is processed into high quality copper cathode in anelectrowinning circuit.

In general, electrowinning of copper consists of the electrolyticdeposition (sometimes called “plating”) of copper onto a cathode and theevolution of oxygen at an anode. In a simple design of an exemplaryelectrowinning unit, a set of cathodes and anodes are set in a reactionchamber containing the copper-containing electrolyte. When the unit isenergized, copper ions are reduced onto the cathode (i.e., plated).Plating of copper typically occurs on copper starter sheets or stainlesssteel blanks. Anodes are quasi-inert in the electrolyte and provide asurface for oxygen evolution. The copper plates produced by theelectrowinning unit can be in excess of 99.99 percent pure.

Purification of copper from the pregnant leach solution by solventextraction has proven to be a successful means of providing aconcentrated copper solution suitable for electrowinning of highly purecopper metal. Direct electrowinning of copper—that is, plating of copperdirectly from the pregnant leach solution without the intervening stepof purification by solvent extraction—is known. However, the copperrecovered by such so-called direct electrowinning processes often is tooimpure for sale or use as is, and thus, generally must be furtherrefined at an additional cost, or may be sold at a discount. Morespecifically, prior art techniques have shown the ability for directelectrowinning of copper to produce a relatively low-quality copperproduct.

An effective and efficient method to recover copper fromcopper-containing materials, especially copper from copper sulfides suchas chalcopyrite and chalcocite, that enables high copper recovery to beachieved at a reduced cost over conventional processing techniques wouldbe advantageous.

SUMMARY OF INVENTION

While the way in which the present invention addresses the deficienciesand disadvantages of the prior art is described in greater detailhereinbelow, in general, according to various aspects of the presentinvention, a process for recovering copper and other metal values from acopper-containing material includes obtaining a copper-containingsolution from, for example, a pressure leaching system, and thenappropriately conditioning the copper-containing solution forelectrowinning. In a preferred aspect of the invention, the compositionof the copper-containing solution is similar to the composition of theelectrolyte produced by a solvent extraction circuit, for example, withrespect to acid and copper concentrations. In accordance with thevarious embodiments of the present invention, however, thecopper-containing solution is not subjected to solvent extraction.

In accordance with an exemplary embodiment of the present invention, aprocess for recovering copper from a copper-containing materialgenerally includes the steps of: (i) providing a feed stream containingcopper-containing material; (ii) subjecting the copper-containing feedstream to atmospheric leaching or pressure leaching to yield acopper-containing solution; (iii) conditioning the copper-containingsolution through one or more chemical or physical conditioning steps;and (iv) electrowinning copper directly from the copper-containingsolution, without subjecting the copper-containing solution to solventextraction. As used herein, the term “pressure leaching” shall refer toa metal recovery process in which material is contacted with an acidicsolution and oxygen under conditions of elevated temperature andpressure.

In accordance with an exemplary embodiment of the present invention, aprocess for recovering copper from a copper-containing materialgenerally includes the steps of: (i) providing a feed stream containingcopper-containing material; (ii) subjecting the copper-containing feedstream to atmospheric leaching or pressure leaching to yield acopper-containing solution; (iii) conditioning the copper-containingsolution through one or more chemical or physical conditioning steps;and (iv) electrowinning copper directly from the copper-containingsolution, without subjecting the copper-containing solution to solventextraction. As used herein, the term “pressure leaching” shall refer toa metal recovery process in which material is contacted with an acidicsolution and oxygen under conditions of elevated temperature andpressure.

In one aspect of a preferred embodiment of the invention, one or moreprocessing steps are used in order to separate copper from the acid in arecycled portion of the lean electrolyte from the direct electrowinningprocess, thus enabling the rejection of a portion of the acid componentfrom the process circuit without rejecting a significant portion thecopper. As discussed in greater detail hereinbelow, a number ofconventional or hereafter devised processes may be utilized to separatecopper from acid in the feed stream. For example, in accordance with oneaspect of an exemplary embodiment of the invention, a copperprecipitation step may be utilized to precipitate solubilized copperfrom a lean electrolyte stream onto the surfaces of solid particles in acopper-containing material stream in advance of the pressure leachingstep, thus separating the copper from the acid solution.

In an aspect of another embodiment of the invention, a recycle circuitis used intermediate to the leaching and electrowinning steps tofacilitate control of the composition of copper-containing solutionentering the electrowinning stage, and to thus enhance the quality ofthe copper recovered therefrom.

In accordance with various preferred aspects of the present invention,by providing for the electrowinning of copper directly from acopper-containing solution without first subjecting thecopper-containing solution to solvent extraction, the present inventionenables lower-cost recovery of copper and eliminates the expensesassociated with solvent extraction, such as specialized reagents,process apparatus and equipment, and energy resources. Furthermore, inaccordance with one preferred aspect of the invention, careful controlof the composition of the copper-containing solution entering theelectrowinning circuit enables production of high quality,uniformly-plated cathode copper.

These and other advantages of a process according to various aspects ofthe present invention will be apparent to those skilled in the art uponreading and understanding the following detailed description withreference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present invention is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present invention, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements and wherein:

FIG. 1 illustrates a flow diagram of a copper recovery process inaccordance with an exemplary embodiment of the present invention; and

FIG. 2 illustrates a flow diagram of a copper recovery process inaccordance with an alternative embodiment of the present invention.

DETAIL DESCRIPTION

The present invention exhibits significant advancements over prior artprocesses, especially other so-called “direct electrowinning” processes,particularly with regard to product quality and process efficiency.Moreover, existing copper recovery processes that utilize a conventionalatmospheric or pressure leaching/solvent extraction/electrowinningprocess sequence may, in many instances, be easily retrofitted toexploit the many commercial benefits the present invention provides.

In one aspect of a preferred embodiment of the invention, the relativelylarge amount of acid generated during the electrowinning stage as acopper-containing electrolyte stream is transported out of the copperrecovery process after a separation step in which substantially all ofthe copper is removed from the acid stream. It is generally economicallyadvantageous to utilize this generated acid stream in some way, ratherthan to neutralize or dispose of it. Thus, as discussed in greaterdetail hereinbelow, the present invention may find particular utility incombination with conventional atmospheric leaching operations, such as,for example, heap leaching, vat leaching, dump or stockpile leaching,pad leaching, agitated tank leaching, and bacterial leaching operations,which often require a substantially continuous acid supply.

In one aspect of an exemplary embodiment of the present invention, afeed stream containing copper-containing material is provided forprocessing. In accordance with the various embodiments of presentinvention, the copper-containing material may be an ore, a concentrate,or any other copper-bearing material from which copper and/or othermetal values may be recovered. The copper in the copper-containingmaterial may be in the form of copper oxides, copper sulfides or othercopper minerals, and the copper-containing material may include anynumber of a variety of other metals, such as, for example, gold,platinum group metals, silver, zinc, nickel, cobalt, molybdenum, rareearth metals, rhenium, uranium and mixtures thereof. Various aspects andembodiments of the present invention prove especially advantageous inconnection with the recovery of copper from copper sulfide ores, suchas, for example, chalcopyrite (CuFeS₂), chalcocite (Cu₂S), bornite(Cu₅FeS₄), and covellite (CuS).

The feed stream of copper-containing material can be provided in anynumber of ways, such that the conditions of the feed stream are suitablefor the chosen processing methods. For example, feed stream conditionssuch as particle size, composition, and component concentrations canaffect the overall effectiveness and efficiency of downstream processingoperations, such as, for example, atmospheric leaching or pressureleaching.

In accordance with a preferred aspect of the invention, the particlesize of the copper-containing feed material is reduced to facilitatefluid transport and to optimize the processing steps of atmospheric orpressure leaching and subsequent metal recovery processes. A variety ofacceptable techniques and devices for reducing the particle size of thecopper-containing material are currently available, such as ball mills,tower mills, ultrafine grinding mills, attrition mills, stirred mills,horizontal mills and the like, and additional techniques may later bedeveloped that may achieve the desired result of increasing the surfacearea of the material to be processed. With regard to one aspect of apreferred embodiment of the invention, such a result is desired becausethe reaction rate during leaching generally increases as the surfacearea of the copper-containing material increases, such that increasingthe fineness of the copper-containing material before subjecting thematerial stream to pressure leaching generally will allow for moremoderate temperature and pressure conditions to be employed within thepressure leaching vessel, and may reduce the residence time of theoxidation reaction during pressure leaching.

FIG. 1 illustrates an exemplary embodiment of the present inventionwherein copper is the metal to be recovered from a copper-containingmaterial, such as a sulfide ore. In preparation for froth flotation, thecopper-containing material feed stream is ground to a particle sizesuitable to liberate mineral-bearing particles from gangue materials. Inone aspect of a preferred embodiment, copper-containing material iscomminuted using, for example, a ball mill, and subjected toconventional flotation techniques and practices. In one aspect of thepresent invention, the copper-containing material has a P80 of less thanabout 250 microns, preferably a P80 from about 75 to about 150 microns,with the optimal size depending on flotation and liberationcharacteristics. The product from flotation preferably has a P80 of lessthan about 150 microns, and more preferably a P80 on the order of fromabout 5 to about 75 microns. Other particle sizes and distributions thatfacilitate fluid transport and subsequent processing may, however, beutilized.

In another aspect of a preferred embodiment of the present invention,the comminuted copper-containing material is combined with a liquid toform a copper-containing material stream 101. Preferably, the liquidcomprises water, but any suitable liquid may be employed, such as, forexample, raffinate, pregnant leach solution, or lean electrolyte. Forexample, a portion of lean electrolyte stream 108 from the directelectrowinning process may be combined with comminuted copper-containingmaterial to form copper-containing material stream 101 (not shown inFIG. 1).

In another aspect of a preferred embodiment of the present invention,the comminuted copper-containing material is combined with a liquid toform a copper-containing material stream 101. Preferably, the liquidcomprises water, but any suitable liquid may be employed, such as, forexample, raffinate, pregnant leach solution, or lean electrolyte. Forexample, a portion of lean electrolyte stream 108 from the directelectrowinning process may be combined with comminuted copper-containingmaterial to form copper-containing material stream 101 (not shown inFIG. 1).

The combination of the liquid with the copper-containing material can beaccomplished using any one or more of a variety of techniques andapparatus, such as, for example, in-line blending or using a mixing tankor other suitable vessel. In accordance with a preferred aspect of thisembodiment, the material stream is concentrated with thecopper-containing material being on the order less than about 50 percentby weight of the stream, and preferably about 40 percent by weight ofthe stream. Other concentrations that are suitable for transport andsubsequent processing may, however, be used.

In accordance with one aspect of the present invention, it is desirableto separate the copper in a recycled stream of lean electrolyte fromelectrowinning from the acid, and also to reduce the amount ofcontaminants in the portion of the stream to be subjected to the metalrecovery process. In such a separation process, the acid that is removedfrom the recycled lean electrolyte stream may be rejected from theprocess circuit, taking with it at least a portion of the metalcontaminants and other soluble impurities from the copper-containingfeed stream and the recycled lean electrolyte stream. Any number ofconventional or hereafter devised separation processes and techniquesmay be useful to achieve the separation of copper from acid in the feedstream. For example, separation processes and/or techniques such asprecipitation, low temperature pressure leaching, acid solventextraction/ion exchange, membrane separation, cementation, pressurereduction, sulfiding, and/or the use of liberator cells may be usefulfor this purpose.

The separation aspect of a preferred embodiment of the inventioncontributes to providing a resultant acid stream that contains arelatively small fraction of copper, which can be used for leaching, pHcontrol, or other applications. Moreover, utilization of a separationprocess in accordance with this aspect of the invention may beparticularly advantageous in that it may enable contaminants from theunrefined copper-containing material stream to be removed from thecopper-containing material stream and incorporated into the resultantacid stream. Because the resultant acid stream is preferably removedfrom the metal recovery process altogether and utilized in remoteoperations, disposed of, or neutralized, the contaminants containedtherein are likewise removed from the metal recovery process and arethus prevented from accumulating in the process stream. This may be asignificant advantage in that such contaminants, particularly metalcontaminants, typically have a deleterious effect on the effectivenessand efficiency of the desired metal recovery process. For example, metalcontaminants and other impurities in the process stream, if notcarefully controlled and/or minimized, can contribute to diminishedphysical and/or chemical properties in the cathode copper produced byelectrowinning, and can thus degrade the copper product and diminish itseconomic value.

Referring again to FIG. 1, in accordance with one aspect of a preferredembodiment of the invention, copper-containing material stream 101 issubjected to a separation, such as, for example, a precipitation step,which, in this exemplary process, serves to precipitate solubilizedcopper from a recycled lean electrolyte stream onto the surfaces ofsolid particles in the copper-containing material stream. As discussedin detail above, this aspect offers an important advantage in that itenables recovery of copper from a lean electrolyte stream that otherwisemay have been lost or would have required additional processing torecover, potentially resulting in significant economic benefits.

In this preferred aspect of the invention, the precipitation stepinvolves the copper-containing material stream being combined with asulfur dioxide (SO₂) stream 109 and a lean electrolyte stream 108 in asuitable processing vessel. For example, in the embodiment illustratedin FIG. 1, lean electrolyte stream 108 may comprise a recycled acidiccopper sulfate stream generated during an electrowinning operation.Other streams, however, preferably copper-rich streams, may also beused. In one aspect of this embodiment of the invention, leanelectrolyte stream 108 has an acid concentration of from about 20 toabout 200 grams/liter, preferably from about 30 to about 150grams/liter, and most preferably from about 50 to about 120 grams/liter.In a further aspect of this embodiment of the invention, leanelectrolyte stream 108 has a copper concentration of from about 20 toabout 55 grams/liter, preferably from about 25 to about 50 grams/liter,and most preferably from about 30 to about 45 grams/liter. In copperprecipitation stage 1010, copper from lean electrolyte stream 108precipitates to form a desired copper-rich concentrate. Preferably,precipitation is carried out such that the copper from the leanelectrolyte precipitates, at least in part, onto the surface ofunreacted copper-containing material particles within stream 101 in theform of copper sulfides, such as, for example, CuS. While not wishing tobe bound by any particular theory, the chemical reaction during thisexemplary copper precipitation step—wherein, for example, thecopper-containing material is primarily chalcopyrite—is believed to beas follows:2Cu⁺²+CuFeS₂+4SO₂+4H₂O→3CuS+3SO₄ ⁻²+8H⁺+Fe⁺²CuFeS₂+Cu⁺²→Fe⁺²+2CuS(possible side reaction)

Other copper minerals and other sulfides react to varying degreesaccording to similar reactions, producing copper precipitates and a weaksulfuric acid by-product. In accordance with a preferred aspect of theinvention, copper separation stage 1010 is carried out at a slightlyelevated temperature, such as from about 70° C. to about 180° C.,preferably from about 80° C. to about 100° C., and most preferably at atemperature of about 90° C. Heating, if necessary, can be effectuatedthrough any conventional means, such as electric heating coils, a heatblanket, process fluid heat exchange, and other ways now known or laterdeveloped. In the exemplary process of FIG. 1, steam generated in otherprocess areas, such as stream 119 from flash tank 1040 or stream 118from pressure leaching stage 1030, may be directed to the processingvessel in copper separation stage 1010 to provide the heat desired toenhance the precipitation process. The residence time for the copperprecipitation process can vary, depending on factors such as theoperating temperature of the processing vessel and the composition ofthe copper-containing material, but typically ranges from about thirty(30) minutes to about 6 hours. Preferably, conditions are selected suchthat significant amounts of copper are precipitated. For example,precipitation rates on the order of about 98% precipitation of copperhave been achieved in processing vessels maintained at about 90° C. forabout 4 hours.

Other parameters to consider when conditioning the copper-containingmaterial feed stream for processing are the fraction of solid particlesin the feed stream and the total volume of the feed stream. Thus, theseor other parameters, such as, for example, temperature, pressure,viscosity, density, composition, and the like, may be suitablyaddressed. Although these parameters may or may not be significant tothe overall efficiency of processing operations downstream in all cases,these parameters can affect equipment size and material specifications,energy requirements, and other important aspects of process design.Thus, calculated adjustment of these stream parameters in advance ofcomplex or resource-intensive processing stages can positively affectthe economic efficiency of the chosen process. Solid-liquid separationsystems, such as, for example, filtration systems, counter-currentdecantation (CCD) circuits, thickeners, and the like are useful inadjusting these parameters and are widely used in the industry.

In one aspect of the embodiment of the invention illustrated in FIG. 1,product stream 102, which generally contains covellite/chalcopyriteparticles and acid, contains a large fraction of acid generated inpressure leaching stage 1030 and electrowinning stage 1070, and the acidgenerated in copper separation stage 1010.

In accordance with a preferred aspect of the invention, thecopper-containing material stream entering the pressure leaching stagecontains from about 10 to about 50 percent solids by weight, preferablyfrom about 20 to about 40 percent solids by weight. To adjust the solidsconcentration of product stream 102 in accordance with the desiredparameters, in accordance with an exemplary embodiment of the invention,product stream 102 is sent to a solid-liquid separation circuit 1020. Inone aspect of a preferred embodiment of the invention, solid-liquidseparation circuit 1020 preferably includes a wash thickener circuit1021 comprising multiple thickener stages arranged in a counter-currentdecantation (CCD) configuration that effectuate separation of asubstantial amount of the acid in the product stream from thecopper-containing solid particles therein. In the illustratedembodiment, the underflow of thickener circuit 1021 is pressure leachingfeed stream 103 and the overflow is acid stream 110. Preferably, acidstream 110 contains only a negligible amount of copper.

Process effluent acid stream 110 may be utilized, processed,neutralized, impounded, and/or disposed of in a variety of ways, theappropriate choice of which is largely dependent upon economic andregulatory factors. In one aspect of the illustrated embodiment, theacid stream can be beneficially used in, for example, an atmosphericleaching operation, where acid is required to leach copper oxide orsulfide minerals. Such a leaching operation may be a heap leach, a vatleach, a tank leach, a pad leach, or any other similar operation. Acidis consumed in these operations through reaction with acid-consumingconstituents in the ore.

In FIG. 2, acid stream 110 from thickener circuit 1021 (FIG. 1) is sentto a conventional atmospheric leach operation 2010. In accordance withone aspect of a preferred embodiment of the invention, atmospheric leachoperation 2010 is a conventional acid-consuming heap leach operation,wherein a subgrade ore 201 is contacted with acid stream 110 and,optionally, other process streams, such as raffinate stream 206 fromdownstream solvent extraction unit 2020. In heap leach operation 2010,the acid percolates downward through the ore heap, solubilizing thecopper in the copper-containing ore in the form of copper sulfate, toform a copper-rich pregnant leach solution (PLS) stream 203. Inconventional atmospheric leach operations, PLS stream 203 is sent to asolvent extraction unit, such as solvent extraction unit 2020 in FIG. 2,to produce a high concentration and relatively pure copper sulfatesolution suitable for electrowinning. In accordance with an alternativeaspect of the present invention illustrated in FIG. 2, PLS stream 203may not be subjected to solvent extraction, but may instead be blendedwith other copper-containing process streams, and the resultant streamthen sent to an electrowinning circuit. For example, all or a portion ofPLS stream 203 (broken line) may be blended with copper-containingsolution stream 106 and lean electrolyte stream 115 in electrolyterecycle tank 1060 (from FIG. 1) to form a resultant product streamsuitable for electrowinning in an electrowinning circuit.

In accordance with a further aspect of this embodiment of the presentinvention, as previously briefly mentioned, acid stream 110advantageously may remove impurities from the process, for example theelectrowinning process. Such impurities include, without limitation,iron, aluminum, magnesium, sodium, potassium and the like, often presentas sulfates. In the absence of removal, such impurities may accumulateto deleterious levels, and, as such negatively impact productionefficiencies and product (e.g. copper cathode) quality. The presence ofsuch impurities in acid stream 110 generally does not negatively impactthe aforementioned handling of acid stream 110.

In accordance with one aspect of a preferred embodiment of the inventionillustrated in FIG. 2, solvent extraction unit 2020 purifiescopper-bearing PLS stream 203 from the heap leach in two unitoperations—an extraction operation, which may have multiple stages,followed by a stripping operation. In the extraction stage, PLS stream203 is contacted with an organic phase consisting of a diluent in whicha copper selective reagent (i.e., the extractant) is dissolved. When thesolutions are contacted, the organic extractant chemically removes thecopper from the PLS, forming an aqueous raffinate stream. The raffinateand organic streams are subsequently separated in a settler. Afterseparation of the organic and aqueous phases in the settler, a portionof the aqueous phase (stream 206) is typically returned to one or moreleaching operations to be reloaded with copper from the ore in theatmospheric leach to form the PLS. The organic stream passes on to thesecond unit operation of the solvent extraction process, the strippingoperation. In the stripping operation, the organic stream is contactedwith a strongly acidic electrolyte. This acidic solution “strips” thecopper from the extractant, leaving the organic phase substantiallydepleted of copper. At least a portion of the loaded strip solutionaqueous phase (stream 204) is advanced to an electrowinning plant 2030as a copper “rich” solution. Aqueous stream 204 is processed inelectrowinning plant 2030 to yield cathode copper 207 and acopper-containing lean electrolyte stream 208, which, in one aspect of apreferred embodiment of the invention, may be recycled in part tosolvent extraction unit 2020.

In accordance with one alternative aspect of the invention, aqueousstream 204 may not be subjected to electrowinning immediately afterleaving the solvent extraction unit, but may instead be blended withother copper-containing process streams, and the resultant stream thensent to an electrowinning circuit. For example, all or a portion ofaqueous stream 204 (broken line) may be blended with copper-containingsolution stream 106 and lean electrolyte stream 115 in electrolyterecycle tank 1060 (from FIG. 1) to form a resultant product streamsuitable for electrowinning in an electrowinning circuit 1070. In suchcases the stripping solutions used in solvent extraction 2020 likelywill be comprised of spent electrolyte from electrowinning circuit 1070.

If effluent acid stream 110 is not used as a by-product reagent orotherwise utilized, the acid may be neutralized using, for example,acid-consuming gangue (i.e., mineral processing tailings) or aneutralizing agent, such as limestone or lime. Neutralizing withacid-consuming gangue can be relatively inexpensive, as the neutralizingreagent is essentially free. On the other hand, neutralizing withlimestone or lime may be less desirable economically, as both thesereagents will incur cost. Nevertheless, should neutralization bedesired, any method for acid neutralization now known or hereafterdevised may be employed.

Referring again to FIG. 1, the underflow slurry from wash thickenercircuit 1021, pressure leaching feed stream 103 in this preferredembodiment of the invention, has a composition of about 40 to about 60percent solids by weight, the balance being a dilute acid solution. Thegeneral composition of the dilute acid solution is dependent upon theratio of process water to acid introduced in the thickener circuit(i.e., the wash ratio).

In a further aspect of the present invention, the conditionedcopper-containing feed stream preferably is subjected to a suitableprocess, such as pressure leaching, to produce a product slurry 104,which comprises a copper-containing solution and a residue 114. Theprocess may be selected as desired, but, in general, enables productionof a copper-containing solution that exhibits copper and acidconcentrations similar to an electrolyte stream resulting from a solventextraction circuit—that is, the copper-containing solution preferably issuitable for processing in an electrowinning circuit. Any suitabletechnique or combination of techniques that yields an appropriatecopper-containing solution without employing solvent extractiontechniques may be used. In a preferred embodiment of the invention, asillustrated in FIG. 1, pressure leaching feed stream 103 is subjected toa pressure leaching stage 1030 to yield a copper-containing productslurry 104.

In accordance with one aspect of this embodiment of the presentinvention, pressure leaching feed stream 103 is transported to asuitable vessel for pressure leaching, which can be any vessel suitablydesigned contain the process components at the desired temperature andpressure conditions for the requisite processing residence time. In apreferred embodiment, a pressure leaching vessel 1031 is employed forthis purpose. Pressure leaching vessel 1031 is preferably amulti-compartment, agitated vessel.

Generally, the chemical conversions that occur during pressure leachingstage 1030 under certain conditions for the solubilization of the copperin copper-containing materials, such as chalcopyrite, chalcocite, orcovellite are as follows:4CuFeS₂+17O₂+4H₂O→4CuSO₄+4H₂SO₄+2Fe₂O₃2Cu2_(S)+5O₂+2H₂SO₄→4CuSO₄+2H₂OCuS+2O₂→CuSO₄

If desired, conditions during pressure leaching can be controlled suchthat a portion of the sulfide sulfur contained in the feed stream isconverted to elemental sulfur instead of sulfate. The fraction ofchalcopyrite and covellite that form sulfur instead of sulfate arebelieved to react according to the following equations:4CuFeS₂+4H₂SO₄+5O₂→4CuSO₄+2Fe₂O₃+8S⁰+4H₂O2CuS+2H₂SO₄+O₂→2Cu⁺²+2SO₄ ⁻²+2H₂O+2S⁰

Pressure leaching, for example in pressure leaching vessel 1031,preferably occurs in a manner suitably selected to promote thesolubilization of copper using these (or other) processes. In general,temperature and pressure in the pressure leaching vessel should becarefully controlled. For example, in accordance with one aspect of theinvention, the temperature of pressure leaching vessel 1031 ismaintained at from about 100° C. to about 250° C., preferably from about140° C. to about 235° C. In accordance with one aspect of one embodimentof the invention, the temperature of pressure leaching vessel 1031 isadvantageously maintained at from about 140° C. to about 180° C. or inthe range of from about 150° C. to about 175° C. In accordance withanother embodiment of the invention, the temperature of pressureleaching vessel 1031 is advantageously maintained between from about200° C. to about 235° C. or in the range of from about 210° C. to about225° C. Furthermore, the total operating pressure in pressure leachingvessel 1031 is necessarily superatmospheric, ranging from about 50 toabout 750 psi. In accordance with one aspect of one embodiment of theinvention, the pressure is advantageously in the range of between fromabout 200 to about 450 psi, and more preferably from about 250 to about400 psi. In accordance with another embodiment of the invention, thepressure is advantageously maintained between from about 400 or about500 to about 700 psi.

During pressure leaching, it is generally desirable to inject oxygeninto the pressure leaching vessel. In one aspect of a preferredembodiment of the invention, during pressure leaching in pressureleaching vessel 1031, sufficient oxygen 112 is injected into the vesselto maintain an oxygen partial pressure in pressure leaching vessel 1031of from about 50 to about 200 psi, preferably from about 75 to about 150psi, and most preferably from about 100 to about 125 psi.

Because pressure leaching of many metal sulfides is a highly exothermicprocess and the heat generated is generally greater than that requiredto heat pressure leaching feed stream 103 to the desired operatingtemperature, cooling liquid 1111 is preferably contacted with pressureleaching feed stream 103 in pressure leaching vessel 1031 duringpressure leaching. Cooling liquid 111 is preferably process water, butcan be any suitable cooling fluid from within the refining process orfrom an outside source. In a preferred embodiment of the invention, asufficient amount of cooling liquid 111 is added to pressure leachingvessel 1031 to yield a solids content in the product slurry 104 rangingfrom about 3 to about 15 percent solids by weight.

The residence time for pressure leaching generally depends on a numberof factors, including the composition of the copper-containing feedstream and the operating pressure and temperature of the pressureleaching vessel. In one aspect of the invention, the residence time forpressure leaching ranges from about thirty minutes to about three hours.

In another aspect of the present invention, the copper-containingsolution is conditioned for electrowinning through one or more chemicaland/or physical processing steps. In much the same way that thecopper-containing material feed stream is conditioned for processing inaccordance with above-described aspects of the invention, thecopper-containing solution intended to be utilized in the electrowinningcircuit of the present invention is conditioned to adjust thecomposition, component concentrations, volume, temperature, and/or otherphysical and/or chemical parameters to desired values. Generally, aproperly conditioned copper-containing solution will contain arelatively high concentration of copper in an acid solution and willcontain few impurities. Preferably, the conditions of copper-containingsolution entering the electrowinning circuit are kept at a constantlevel to enhance the quality and uniformity of the cathode copperproduct.

In a preferred aspect of the invention, conditioning of acopper-containing solution for electrowinning begins by adjustingcertain physical parameters of the product slurry from the previousprocessing step. In a preferred embodiment of the invention wherein theprevious processing step is pressure leaching, it is desirable to reducethe temperature and pressure of the product slurry. A preferred methodof so adjusting the temperature and pressure characteristics of thepreferred product slurry is atmospheric flashing.

Thus, in accordance with a preferred aspect of the embodimentillustrated in FIG. 1, product slurry 104 from pressure leaching vessel1031 is flashed in an atmospheric flash tank 1040 or other suitableatmospheric system to release pressure and to evaporatively cool theproduct slurry 104 through the release of steam to form a flashedproduct slurry 105. Flashed product slurry 105 preferably has atemperature ranging from about 90° C. to about 101° C., a copperconcentration of from about 40 to about 75 grams/liter, and an acidconcentration of from about 20 to about 100 grams/liter. In one aspectof the invention, however, flashed product slurry 105 also contains aparticulate solid residue containing, for example, the iron oxideby-product of pressure leaching, other by-products, precious metals andother components that are undesirable for a feed stream to anelectrowinning circuit. Thus, in accordance with the same principlesdiscussed above, it is desirable to subject the flashed product slurryto a solid-liquid separation process, such that the liquid portion ofthe slurry—the desired copper-containing solution—is separated from thesolid portion of the slurry—the undesired residue.

Referring again to FIG. 1, in the illustrated embodiment of theinvention flashed product slurry 105 is directed to a solid-liquidseparation stage 1050, such as a CCD circuit 1051. In an alternativeembodiment of the invention, solid-liquid separation stage 1050 maycomprise, for example, a thickener or a filter. A variety of factors,such as the process material balance, environmental regulations, residuecomposition, economic considerations, and the like, may affect thedecision whether to employ a CCD circuit, a thickener, a filter, orother suitable device in solid-liquid separation stage 1050. In oneaspect of a preferred embodiment of the invention, CCD circuit 1051 usesconventional countercurrent washing of the residue stream with washwater 113 to recover leached copper to the copper-containing solutionproduct and to minimize the amount of soluble copper advancing to eitherprecious metal recovery processes or residue disposal. Preferably, largewash ratios are utilized to enhance the effectiveness of solid-liquidseparation stage 1050—that is, relatively large amounts of wash water113 are added to the residue in CCD circuit 1051. Preferably, thesolution portion of the residue slurry stream is diluted by wash water113 in CCD circuit 1051 to a copper concentration of from about 5 toabout 200 parts per million (ppm) in the solution portion of residuestream 114.

Depending on its composition, residue stream 114 from liquid/solidseparation stage 1050 may be impounded, disposed of, or subjected tofurther processing, such as, for example, precious metal recovery. Forexample, if residue stream 114 contains economically significant amountsof gold, silver, and/or other precious metals, it may be desirable torecover this gold fraction through a cyanidation process or othersuitable recovery process. If gold or other precious metals are to berecovered from residue stream 114 by cyanidation techniques, the contentof contaminants in the stream, such as elemental sulfur, amorphous ironprecipitates, and unreacted copper minerals, is preferably minimized.Such materials may promote high reagent consumption in the cyanidationprocess and thus increase the expense of the precious metal recoveryoperation. As mentioned above, it is therefore preferable to use a largeamount of wash water or other diluent during the solid-liquid separationprocess to maintain low copper and acid levels in the solids-containingresidue stream in an attempt to optimize the conditions for subsequentprecious metal recovery.

As previously noted, careful control of the conditions of acopper-containing solution entering an electrowinning circuit—especiallymaintenance of a substantially constant copper composition—can enhancethe quality of the electrowon copper by, among other things, enablingeven plating of copper on the cathode and avoidance of surface porosityin the cathode copper, which degrades the copper product and thus maydiminish its economic value. In accordance with this aspect of theinvention, such process control can be accomplished using any of avariety of techniques and equipment configurations, so long as thechosen system and/or method maintains a sufficiently constant feedstream to the electrowinning circuit.

Referring again to FIG. 1, in a preferred aspect of the invention,copper-containing solution stream 106 from solid-liquid separation stage1050 is sent to an electrolyte recycle tank 1060. Electrolyte recycletank 1060 suitably facilitates process control for electrowinningcircuit 1070, as will be discussed in greater detail below.Copper-containing solution stream 106, which generally contains fromabout 40 to about 70 grams/liter of copper and from about 15 to about100 grams/liter acid, is preferably blended with a lean electrolytestream 115 in electrolyte recycle tank 1060 at a ratio suitable to yielda product stream 107, the conditions of which may be chosen to optimizethe resultant product of electrowinning circuit 1070.

Referring briefly to an alternative embodiment of the inventionillustrated in FIG. 2, an additional lean electrolyte stream 205 may beblended with lean electrolyte stream 115 and copper-containing solutionstream 106 in electrolyte recycle tank 1060 to produce product stream107 in accordance with the process control principles discussed inconnection with the embodiment illustrated in FIG. 1. In one aspect ofthis alternative embodiment, lean electrolyte stream 205 preferably hasa composition similar to that of lean electrolyte stream 115. Further,as discussed above, other streams may be introduced to electrolyterecycle tank 1060 for blending, such as, for example, PLS stream 203(FIG. 2).

Referring again to FIG. 1, preferably, the copper composition of productstream 107 is maintained substantially constant. While product stream107 may contain a copper concentration up to the copper solubility levelunder the prevailing conditions, preferably product stream 107 has acopper concentration of about 20 to about 80 grams/liter, and morepreferably of about 30 to about 60 grams/liter, and often above 40grams/liter. In one aspect of an exemplary embodiment of the invention,control valves are positioned on each of the pipelines feeding leanelectrolyte stream 115 and copper-containing solution stream 106 toelectrolyte recycle tank 1060 to facilitate blending control within thetank.

With reference to FIG. 1, copper from the product stream 107 is suitablyelectrowon to yield a pure, cathode copper product. In accordance withthe various aspects of the invention, a process is provided wherein,upon proper conditioning of a copper-containing solution, a highquality, uniformly-plated cathode copper product 116 may be realizedwithout subjecting the copper-containing solution to a solventextraction process prior to entering the electrowinning circuit.

As those skilled in the art are aware, a variety of methods andapparatus are available for the electrowinning of copper and other metalvalues, any of which may be suitable for use in accordance with thepresent invention, provided the requisite process parameters for thechosen method or apparatus are satisfied. For the sake of convenienceand a broad understanding of the present invention, an electrowinningcircuit useful in connection with various embodiments of the inventionmay comprise an electrowinning circuit, constructed and configured tooperate in a conventional manner. The electrowinning circuit may includeelectrowinning cells constructed as elongated rectangular tankscontaining suspended parallel flat cathodes of copper alternating withflat anodes of lead alloy, arranged perpendicular to the long axis ofthe tank. A copper-bearing leach solution may be provided to the tank,for example at one end, to flow perpendicular to the plane of theparallel anodes and cathodes, and copper can be deposited at the cathodeand water electrolyzed to form oxygen and protons at the anode with theapplication of current. As with conventional electrowinning cells, therate at which direct current can be passed through the cell iseffectively limited by the rate at which copper ions can pass from thesolution to the cathode surface. This rate, called the limiting currentdensity, is a function of factors such as copper concentration,diffusion coefficient of copper, cell configuration, and level ofagitation of the aqueous solution.

The general chemical process for electrowinning of copper from acidsolution is believed to be as follows:2CuSO₄+2H₂O→2Cu⁰+2H₂SO₄+O₂Cathode half-reaction: Cu²⁺+2e⁻→Cu⁰Anode half-reaction: 2H₂O→4H⁺+O₂+4e⁻

Turning again to FIG. 1, in a preferred embodiment the invention,product stream 107 is directed from electrolyte recycle tank 1060 to anelectrowinning circuit 1070, which contains one or more conventionalelectrowinning cells.

In accordance with a preferred aspect of the invention, electrowinningcircuit 1070 yields a cathode copper product 116, optionally, an off gasstream 117, and a relatively large volume of copper-containing acid,herein designated as lean electrolyte streams 108 and 115. As discussedabove, in the illustrated embodiment of the invention, lean electrolytestreams 108 and 115 are directed to copper precipitation stage 1010 andelectrolyte recycle tank 1060, respectively. Lean electrolyte streams108 and 115 generally have a lower copper concentration than productstream 107, but typically have a copper concentration of less than about40 grams/liter.

The present invention has been described above with reference to anumber of exemplary embodiments. It should be appreciated that theparticular embodiments shown and described herein are illustrative ofthe invention and its best mode and are not intended to limit in any waythe scope of the invention as set forth in the claims. Those skilled inthe art having read this disclosure will recognize that changes andmodifications may be made to the exemplary embodiments without departingfrom the scope of the present invention. For example, although referencehas been made throughout to copper, it is intended that the inventionalso be applicable to the recovery of other metals from metal-containingmaterials. Further, although certain preferred aspects of the invention,such as techniques and apparatus for conditioning process streams andfor precipitation of copper, for example, are described herein in termsof exemplary embodiments, such aspects of the invention may be achievedthrough any number of suitable means now known or hereafter devised.Accordingly, these and other changes or modifications are intended to beincluded within the scope of the present invention, as expressed in thefollowing claims.

1. A method for recovering copper from a copper-containing materialcomprising the steps of: providing a feed stream comprising acopper-containing material and acid; separating at least a portion ofsaid acid from said copper-containing material in said feed stream toyield a leaching feed stream comprising a copper-bearing material and anacid stream; leaching at least a portion of said leaching feed stream toyield a copper-containing product stream; conditioning saidcopper-containing product stream without the use of solvent extractiontechniques to yield a copper-containing solution suitable forelectrowinning; electrowinning copper from at least a portion of saidcopper-containing solution to yield cathode copper and a leanelectrolyte stream.
 2. The method of claim 1, wherein said step ofproviding a feed stream comprising a copper-containing materialcomprises providing a feed stream comprising a copper sulfide ore orconcentrate.
 3. The method of claim 1, wherein said separating stepcomprises reacting at least a portion of the copper in acopper-containing electrolyte stream in the presence of sulfur dioxide,whereby at least a portion of said copper in said copper-containingelectrolyte stream precipitates as copper sulfide onto at least aportion of the copper-containing material in said feed stream.
 4. Themethod of claim 1, wherein said leaching step comprises pressureleaching at least a portion of said leaching feed stream at atemperature of from about 100 to about 250° C.
 5. The method of claim 1,wherein said copper-containing product stream comprises acopper-containing solution and a residue, and wherein said conditioningstep comprises subjecting at least a portion of said copper-containingproduct stream to solid-liquid separation, wherein at least a portion ofsaid copper-containing solution is separated from said residue.
 6. Themethod of claim 5, wherein said conditioning step further comprisesblending at least a portion of said copper-containing solution with atleast a portion of one or more copper-containing streams to achieve adesired copper concentration in said copper-containing solution.
 7. Themethod of claim 5, wherein said conditioning step further comprisesblending at least a portion of said copper-containing solution with atleast a portion of one or more copper-containing streams to achieve acopper concentration of from about 20 to about 75 grams/liter in saidcopper-containing solution.
 8. The method of claim 1 further comprisingthe step of using at least a portion of said acid stream yielded fromsaid separating step in at least one of heap leaching, vat leaching,dump leaching, stockpile leaching, pad leaching, agitated tank leaching,or bacterial leaching operations.
 9. The method of claim 1 furthercomprising the step of recycling at least a portion of said leanelectrolyte stream to the separating step.
 10. The method of claim 3further comprising the step of recycling at least a portion of said leanelectrolyte stream to the separating step.
 11. The method of claim 1further comprising the step of recycling at least a portion of said leanelectrolyte stream to the conditioning step.
 12. The method of claim 5further comprising the step of recycling at least a portion of said leanelectrolyte stream to the conditioning step.
 13. The method of claim 1further comprising the steps of: recycling a portion of said leanelectrolyte stream to the separating step, and recycling a portion ofsaid lean electrolyte stream to the conditioning step.
 14. The method ofclaim 3 further comprising the steps of: recycling a portion of saidlean electrolyte stream to the separating step, and recycling a portionof said lean electrolyte stream to the conditioning step.
 15. The methodof claim 5 further comprising the steps of: recycling a portion of saidlean electrolyte stream to the separating step, and recycling a portionof said lean electrolyte stream to the conditioning step.
 16. The methodof claim 1 further comprising the step of reducing the amount of acid insaid leaching feed stream using a solid-liquid separation device. 17.The method of claim 16, wherein said step of reducing the amount of acidin said leaching feed stream further comprises reducing the impuritiesin said leaching feed stream.
 18. The method of claim 1, wherein saidconditioning step comprises controlling the copper concentration of saidcopper-containing solution such that the copper concentration of saidcopper-containing solution entering the electrowinning step ismaintained at a level of about 40 grams/liter.
 19. The method of claim1, wherein said step of providing a feed stream comprisingcopper-containing material comprises providing a feed stream comprisingcopper sulfide ore or concentrate having a P80 of from about 5 to about75 microns.
 20. The method of claim 1 further comprising the step ofutilizing said lean electrolyte in a solvent extraction operation.